1. Field of the Invention
The present invention refers to a removable device for attaching two mechanical parts, comprising a pin removably locking a first part with respect to a second part, a retainer member associated to the pin and a resiliently loaded tension member, which collaborate to prevent the pin from coming out of its lock position.
2. Description of Related Art
Excavating machines and the like, such as those used in public works and mining, are used to pull out, move and load earth and stones. These machines are usually provided with a bucket joined to a mechanical arm. The bucket is provided with a beveled lip or blade on a front edge intended for striking against and penetrating the earth and stone mass. It is usual to mount teeth associated to the blade projecting forwardly therefrom to prevent excessive wear of the blade and to aid in penetrating the earth. However, said blades are also subjected to wear and breaks, whereby they must often be replaced and furthermore, depending on the work which the machine is to perform, it may be desirable to change the type or shape of the teeth. To facilitate said replacement, fixed to the blade of the bucket in a more or less permanent manner there is a tooth bar and teeth, such that each tooth is removably mounted on the tooth bar by means of a pin. Said pin usually traverses the holes of the tooth and a passage traversing the tooth bar in order to fix the tooth to the tooth bar.
A retainer device is used to prevent the pin from coming out of its assembly position, fixing the pin in its said assembly position. The retainer device usually includes resilient members which usually apply a force pushing the pin towards its assembly position. When the usual arrangements operate under difficult conditions, the pin has the tendency to be displaced against the pushing force of the retainer device. Then the pin can come out of the tooth bar, the pin and tooth possibly being lost. The loss of a tooth and/or pin may be very important according to the operating site thereof, such as mines or quarries for example, since they may damage other machines, such as crushers, operating in the same production site as the machine using the tooth.
U.S. Pat. No. 4,918,843 discloses an arrangement in which the retainer device is a spring washer which is placed in a cavity of the tooth bar defining a housing receiving said washer and positions it concentrically with respect to the corresponding holes of the tooth and the tooth bar, said washer operating and therefore being deformed in the direction perpendicular to the axial axis of the pin. The diameter of the pin is greater than that of the hole of the washer, such that the pin fits into the washer by means of a recess existing on the surface of the pin when a mechanical stress is applied, usually consisting of striking the pin with a hammer or mallet. This requirement of striking the pin in order to fit it into the washer is evidently uncomfortable and arduous since it is usually necessary to strike the pin horizontally, a difficult operation since the space between tooth bars located on the blade of a bucket is limited, requiring the use of auxiliary tools which only make the assembly and removal of the pin more difficult, increasing the risk of an accident for the operator or operators. This retainer device is affected by the quality of the material of the spring washer used since the pin is retained by the same and the retention of the pin will be more or less reliable according to the same. The recess existing in the pin for inserting the washer likewise weakens the pin, the latter possibly breaking due to the work carried out by the tooth-tooth bar assembly and the stress concentration in said recess.
U.S. Pat. No. 5,983,534 discloses a lock system for the pin which is rotary and does not require hammering. In this system, the pin incorporates a resilient member able to exert a force against one portion of the tooth or tooth bar for the purpose of tightening the coupling between both, and a resiliently loaded retainer member radially projecting from a cylindrical wall of the pin and susceptible to being introduced in a cavity of the tooth or tooth bar when the pin, once inserted, is rotated a predetermined angle by means of the application of a tool on an axial end of the pin. A notch allows the introduction of the retainer member when the pin is axially inserted into a passage defined by both the tooth and tooth bar when they are coupled. Once the pin is inserted, a ramped surface acts as a cam to push the retainer member inwardly of the pin as the latter is rotated until reaching the angular position of said cavity, where the retainer member is shot into the cavity due to the effect of said resilient loading. The removal thereof is provided for by either breaking of the retainer member due to the action of striking with a hammer in the axial direction on the pin or the collaboration of inclined surfaces of the housing with corresponding inclined surfaces of the head of the retainer member to push the latter inwardly, either by an axial force exerted on the pin, or by applying a turning torque thereto.
This arrangement entails great complexity for the pin, since it incorporates two moving parts housed and retained in respective cavities of the body of the pin and resiliently loaded by means of coil springs, which negatively affects its production cost. Furthermore, the moving parts and resilient springs housed in the pin are highly susceptible to being affected by the accumulation of dust and earth, which combined with moisture can form a clay-type paste which may lock the springs and the movement possibilities of the moving parts when it dries, which entails the need to destroy them by hammering when it is necessary to remove the teeth.
In this type of systems, the stresses required for removal exceed assembly stresses since in addition to the difficulties of the design and construction, removal is affected because during operation, the pin and retainer member may become deformed and earth can additionally be introduced in the housing of the pin, making its extraction difficult.